You could always use sleep to simulate what you need. E.G.

while (1) {
   # do stuff
   sleep(60*60*3);   # sleep for three hours
}
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This does use up memory (and any open files, etc) while the script is sleeping, but doesn't use up CPU. You could easily have the "do stuff" section simply call another script, so you have less to worry about in terms of keeping resources booked in your main script.

--JAS